Benzimidazole anthelmintic agents

ABSTRACT

##STR1## Benzimidazole anthelmintic agents of formula (I) and their non-toxic salts in which R is H, CO 2  (C 1  -C 10  alkyl), --CO 2  (cholester-3-yl) or --CO 2  (CH 2 )COOH or --CO 2  (CH 2 ) n  CO 2  (C 1  -C 6  alkyl), n=1 to 10, R 1  is optionally substituted benzoyl, phenyloxy, phenylthio, phenyisulfonyl, phenylsulfinyl, phenylsulfonyloxy, alkylthio, alkylsulfinyl, alkylsulfonyl, cycloalkylcarbonyl or is selected from a variety of heterocyclic groups and R 2  and R 3  are independently --CO 2  (C 1  -C 4  alkyl).

This application is a 371 application of PCT/EP93/00422 filed Feb. 23,1993.

The present invention relates to certain benzimidazole anthelminticagents which, quite unexpectedly, are topically and parenterally activeand are thus suitable for transdermal and parenteral (especiallyintramuscular) administration.

These benzimidazole derivatives are represented by the formula: ##STR2##and their non-toxic salts, in which R is H, --CO₂ (C₁ -C₁₀ alkyl), --CO₂(cholester-3-yl) or a group of the formula --CO₂ (CH₂)_(n) COOH or --CO₂(CH₂)_(n) CO₂ (C₁ -C₆ alkyl) in which n is an integer of from 1 to 10;

R¹ is either (i) benzoyl, phenyloxy, phenylthio, phenylsulfinyl,phenylsulfonyl, phenylsulfonyloxy, C₁ -C₆ alkylthio, C₁ -C₆alkylsulfinyl, C₁ -C₆ alkylsulfonyl or (C₃ -C₇ cycloalkyl)carbonyl, saidphenyl groups, and the phenyl portion of said benzoyl group, optionallyhaving 1 to 3 substituents each independently selected from halo, C₁ -C₄alkyl, halo(C₁ -C₄ alkyl), C₁ -C₄ alkoxy, C₁ -C₄ alkylthio, C₁ -C₄alkylsulfinyl, C₁ -C₄ alkylsulfonyl, C₂ -C₄ alkanoyl, nitro,isothiocyanato, and cyano; or (ii) a group of the formula: ##STR3##where X is O,S,SO,SO₂ or NR⁴ in which R₄ is hydrogen; C₁ -C₄ alkyl,phenyl or phenyl(C₁ -C₄ alkyl), said phenyl groups being optionallysubstituted by 1 or 2 substituents each independently selected from C₁-C₄ alkyl, halo, hydroxy and C₁ -C₄ alkoxy; and R₅ is H, C₁ -C₄ alkyl,halo, hydroxy or C₁ -C₄ alkoxy; ##STR4## R¹ being in the 5(6)-positionwhen R is H, and in the 5-or 6-position when R is other than H;

and R² and R³ are each independently --CO₂ (C₁ -C₄ alkyl).

Preferred alkyl and alkoxy groups have 1 to 4 carbon atoms.

n is preferably an integer of from 3 to 6.

R is preferably H, --CO₂ (C₁ -C₈ alkyl), --CO₂ (cholester-3-yl), --CO₂(CH₂)_(n) COOH or --CO₂ (CH₂)_(n) CO₂ --(C₁ -C₄ alkyl) where n is aninteger of from 3 to 6.

R is most preferably H, --CO₂ (C₁ -C₄ alkyl).

R¹ is preferably C₁ -C₄ alkylthio, C₁ -C₄ alkylsulphinyl, phenylthio,phenylsulfinyl, benzoyl optionally substituted by halo,phenylsulfonyloxy optionally substituted by halo, or1,2-benzisoxazol-3-yl.

More preferably, R¹ is benzoyl, 4-fluorobenzoyl,4-fluorophenylsulfonyloxy, n-propylthio, n-propylsulfinyl, phenylthio,phenylsulfinyl, or 1,2-benzisoxazol-3-yl.

Most preferably, R¹ is n-propylthio;

R² and R³ are preferably the same and are both most preferably --CO₂CH₃.

Alkyl, alkoxy, alkanoyl, alkenyl and alkynyl groups, when appropriate,can be straight or branched chain. "Halo" means F, Cl, Br or I.

Suitable non-toxic acid addition salts, suitable for veterinary use, arefor example the hydrochloride, hydrobromide, and sulphate salts. Thesecan all be prepared conventionally.

The benzimidazoles of the formula (I) and their salts are in particularanthelmintics suitable for the control of parasitic diseases in bothhuman and non-human animals such as sheep, cattle and domestic pets. Thecompounds exhibit activity against mature and immature parasitic formsof, for example, nematodes, trematodes and cestodes such as arerepresented by Trichostrongylus, Dictyocaulus, Ostertagia, Nematodirus,Stronglyoides, Trichuris, Haemonchus, Cooperia, Dirofilaria, Toxocara,Trichuris, Fasciola and Monezia species.

Efficient control of these species is achieved by introducing into saidanimals circulatory system an anthelmintically-effective amount of acompound of the formula (I) or a salt thereof. In the case of thesecompounds, it has been unexpectedly found that this control can beachieved by percutaneous absorption and/or penetration from a liquid orcream formulation applied directly to the animals' skin. Such liquidformulations are known as "pour-on formulations". Such pour-onformulations are characterised in that the active ingredient, i.e. thecompound of the formula (I) or a salt thereof, is dissolved, emulsifiedor suspended in a suitable solvent or solvent mixture which is tolerableby the skin and non-toxic to the animal, optionally with certainauxiliary ingredients.

To prepare pour-on formulations, the compounds of the formula (I) andtheir salts are formulated in a conventional manner by mixing them withcarriers which are effective in penetrating the skin, the compound (I)then being absorbed by the animal through the skin and transmittedsystemically throughout the animal.

The pour on formulation contains:

1. a non volatile drug solvent or solvent mixture which may includesolvents normally classed as transdermal penetration enhancers, and,optionally, one or more of the following:

2. a solvent with the specific role of enhancing transdermal penetrationif such a solvent is not already present performing function 1 as themain drug solvent;

3. an accessory spreading agent if this auxiliary function is notperformed adequately by the drug solvent (1) and any transdermalpenetration enhancer (2);

4. a volatile solvent. This volatile solvent may aid the spreading anddistribution of components 1 and 2, adjust the formulation to aconvenient dosing volume, and ensure solubility and miscibility of theformulation in extreme storage conditions;

and 5. further adjuvants, where necessary; to ensure chemical stabilityin storage and use, to increase the viscosity of the formulation toprevent run off, to deter other animals from licking the composition offthe treated animal, and to protect the skin from undesirable irritation.

Suitable drug solvents (1) are selected to achieve adequate solubilityfrom:

Spreading oils--silicone oils, isopropyl myristate, isopropyl palmitate,caprylic/capric acid triglyceride, saturated triglycerides of naturallyoccuring fatty acids, fatty acid esters (e.g. ethyl oleate), and fattyacid esters which correspond to synthetic anatine uropygial gland fat.

Aliphatic hydrocarbons--e.g. light paraffin oil.

Hydroxylic solvents--less volatile alcohols (e.g. hexanol, octanol),propylene glycol, polypropylene glycols, ethylene glycol, diethyleneglycol, glycerols and ether and or ester substituents of these solvents(e.g. Triacetin), benzyl alcohol and carboxylic acid esters (e.g. benzylbenzoate), butyl acetate, propylene carbonate and ethyl lactate.

Polyalkoxylated solvents--Polyethylene glycols, polyglycol ethers and oresters e.g. 2-(2-alkoxy)ethoxyethanols and 2-(2-alkoxy)ethoxyethylalkanoates.

Vegetable oils--not included in the definition of spreading oils e.g.corn, sesame, olive, pine, linseed, cottonseed and ground nut oil.

Penetration enhancing agents (2)--

(a) e.g. dimethylsulphoxide, dimethylformamide and dimethylacetamide;

(b) Pyrrolidones. In particular 2-pyrrolidone, N-methylpyrrolidone, and1 or 5 and 1,5 alkyl substituted pyrrolidones e.g.1,5-dimethyl-2-pyrrolidone or carboxylic acid substituted pyrrolidones;

(c) alkylsulphoxides, sugar esters and phosphine oxides; and

(d) azacycloalkan-2-ones.

While these solvents may be used in miscible combinations, miscibilitymay be achieved by incorporation of a ternary solvent, if required, toprovide adequate drug solubility.

Accessory spreading agents (3) comprising spreading oils (if these arenot used as the main drug solvent as previously listed in (1)) orsurface active agents where the term surface active agent is used tocover materials variously called wetting agents, emulsifying agents anddispersing agents.

These include:

Non-ionic water soluble emulsifiers such as alkylaryl polyglycol ethers,polyoxyethylene alkylaryl ether, alkylpolyglycol ethers, polyoxyethyleneesters and ethers, polyoxyethylene sorbitan mono fatty acid esters,sorbitan mono fatty acid esters, ethoxylated nonyl phenols,isooctylphenol, polyethoxyethanol and polyethoxylated castor oil(Cremophor EL^(R)). Anionic surfactants including soaps, fatty sulphateesters (e.g. dodecyl Na sulphate), fatty aromatic sulphonates (e.g.alkylbenzenesulphonates), more complex fatty sulphonates such as theamide condensation product of oleic acid and N-methyltaurine, the sodiumsulphonate of dioctylsuccinate and the disodium ethoxylated nonylphenolhalf ester of sulphosuccinic acid. Cationic agents such ascetyltrimethylammonium bromide may also be used as well as ampholyticsurfactants such as di-Na-N-lauryl betaiminodiopropionate or lecithin.Suitable volatile solvents (4) include:

Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone andcyclohexanone; simple alcohols (in particular methanol, ethanol and[especially] isopropylalcohol); straight and branched alkylethers (e.g.dibutyl diisopropyl ether), tetrahydrofuran, glycol ethers and straightand branched chain alkyl acetates (e.g. isopropyl acetate) and otheresters such as lactic acid ethyl ester; aromatic hydrocarbons such asxylene, benzene, toluene, alkylnaphthalenes and chlorobenzenes; andaliphatic hydrocarbons such as paraffins of chain length 6-20 andhalogenated aliphatic hydrocarbons.

Appropriate auxiliary additives (5) include:

Stability enhancers--antioxidants e.g. ascorbic acid, butylatedhydroxyanisole and butylated hydroxytoluene.

Colourants--inorganic pigments, iron (II) oxide, titanium dioxide,Prussian blue; organic dyestuffs e.g. alizarin based, azo dye-based ormetal phthalocyanine-based dyestuffs.

Adhesion promoters--carboxymethylcellulose, methylcellulose and othercellulose and starch derivatives, polyacrylates, alginates, gelatines,gum arabic, polyvinylpyrrolidone, copolymers of methylvinyl ether andmaleic anhydride, polyethylene glycols, paraffins, oils and waxes,hydrogenated castor oil, lecithins and synthetic phospholipids.

Oral deterrents--such as bitter aloes.

Emolients--such as lanolin.

The drug is dissolved in typical formulations which contain 1-100% ofthe main drug solvents, usually not more than 70% and ideally not morethan 20%. The rest of the formulation is composed in the main by thevolatile solvent which may comprise 0-99% of the formulation andpreferably not less than 30%. Further transdermal penetration enhancers(0-33%), accessory spreading agents (0-25%) and adjuvants (0-5%) areadded as required.

Preferred formulations for the actives were selected from typicalformulations.

Examples of some typical formulations are:

    ______________________________________                                        Ingredient               % Composition                                        ______________________________________                                        Formulation 1                                                                 2-(2-Butoxyethoxy) ethanol                                                                             100                                                  Formulation 2                                                                 2-(2-Butoxyethoxy) ethanol                                                                              5                                                   Propan-2-ol              95                                                   Formulation 3                                                                 Ethyl oleate             50                                                   Isopropyl acetate        50                                                   Formulation 4                                                                 Dimethylsulphoxide       20                                                   Xylene                   80                                                   Formulation 5                                                                 Cetyl 2 ethylhexanoate/  10                                                   stearyl 2-ethylhexanoate blend                                                Propan-2-ol              90                                                   Formulation 6                                                                 PEG 300                  60                                                   iso-octylphenoxypolyethoxyethanol                                                                      10                                                   e.g. Triton X-100.sup.R                                                       Propan-2-ol              30                                                   Formulation 7                                                                 Propylene glycol         50                                                   Hydroxypropyl cellulose (MW 1 × 10.sup.6 Dalton)                                                   0.5                                                e.g. Klucel HPC HF.sup.R                                                      Butylated hydroxyanisole 0.02% w/v                                            Ethanol                  to 100%                                              Formulation 8                                                                 Propylene glycol          5                                                   Sodium Erythrosine       0-0.01% w/v                                          Methanol                 to 100%                                              Formulation 9                                                                 Triacetin                60                                                   Isopropyl acetate        40                                                   ______________________________________                                    

The pour-on formulations typically contain the active compound (I) saltthereof in an amount of from 0.5% wt/vol to 60% wt/vol. A typicalpour-on formulation would contain 1 to 50 mg of the active ingredientper kg of animal body weight in, say, 0.01-1 ml per kg body weight ofthe animal. Typically the formulation is simply poured on the animal.Concentrated formulations are often referred to as "spot-on"formulations, which are spotted onto the animal.

The compounds of formula (I) are administered as a formulationappropriate to the specific use envisaged and to the particular speciesof host animal being treated and the parasite involved. For use as ananthelmintic the compounds may be administered orally in the form of acapsule, bolus, tablet or drench or as a pour-on formulation, oralternatively, they can be administered by injection (e.g.subcutaneously, intramuscularly or intravenously) or as an implant. Suchformulations are prepared in a conventional manner in accordance withstandard veterinary practice. Thus. capsules, boluses or tablets may beprepared by mixing the active ingredient with a suitable finely divideddiluent or carrier additionally containing a disintegrating agent and/orbinder such as starch, lactose, talc, magnesium stearate etc. Oraldrenches are prepared by dissolving or suspending the active ingredientin a suitable medium. Injectable formulations may be prepared in theform of a sterile solution which may contain other substances, forexample, enough salts or glucose to make the solution isotonic withblood. Acceptable liquid carriers include the vegetable oils such assesame oil and the like, glycerides such as triacetin and the like,esters such as benzyl benzoate, isopropyl myristate and fatty acidderivatives of propylene glycol and the like, as well as organicsolvents such as pyrrolidone, glycerol formal and the like. Theformulations are prepared by dissolving or suspending the activeingredient in the liquid carrier such that the final formulationcontains from 0.5 to 60% by weight of the active ingredient. Theseformulations will vary with regard to the weight of active compounddepending on the species of host animal to be treated, the severity andtype of infection and the body weight of the host. For parenteral andoral administration, typical dose ranges of the active ingredient are1-50 mg per kg of body weight of the animal. Pour-on formulations havebeen previously described.

As an alternative the compounds may be administered with the animalfeedstuff and for this purpose a concentrated feed additive or premixmay be prepared for mixing with the normal animal feed.

The compounds of the invention are highly active antiparasitic agentshaving utility not only as anthelmintics, but as ectoparasiticides,insecticides and antiprotozoal agents.

Thus the compounds are effective in treating a variety of conditionscaused by endoparasites including, in particular, helminthiasis which ismost frequently caused by a group of parasitic worms described asnematodes, cestodes and trematodes, and which can cause severe economiclosses in swine, sheep, horses and cattle as well as affecting domesticanimals and poultry. The compounds are also effective against othernematodes which affect various species of animals including, forexample, Dirofilaria, Toxocara, Ancyclostoma, Dipylidium, Echinococcusand Taenia in dogs and various parasites which can infect humansincluding gastro-intestinal parasites such as Ancvlostoma, Necator,Ascaris, Strongyloides, Trichinella, Capillaria, Trichuris, Enterobiusand parasites which are found in the blood or other tissues and organssuch as filarial worms and the extra intestinal stages of Strongyloidesand Trichinella.

The compounds are also of value in treating ectoparasite infectionsincluding in particular arthropod ectoparasites of animals and birdssuch as ticks, lice, fleas, blowfly, biting insects and migratingdipterous larvae which can affect cattle and horses.

The compounds are also insecticides active against household pests suchas the cockroach, clothes moth, carpet beetle and the housefly.

For use as an insecticide the compounds can be applied as sprays, dusts,emulsions and the like.

The compounds of the formula (I) in which R is H, or in which R and R³are the same and are --CO₂ (C₁ -C₄ alkyl) can be prepared by alkylatingan optionally protected 5(6)- benzimidazole of the formula: ##STR5##where R¹ is in the 5-(6-) position, R¹ and R² being as defined forformula (I), and X is H or an amino-protecting group, with a compound ofthe formula:

    Q--R.sup.3 or R.sup.3 --O--R.sup.3                         (III)

where Q is a suitable leaving group, such as chloro, and R³ is asdefined for formula (I), followed by removal of the amino-protectinggroup, if present, to produce a compound (I) in which R is H.

A preferred amino-protecting group is t-butoxycarbonyl.

The reaction is preferably carried out in the presence of an organic orinorganic base such as triethylamine, pyridine or potassium carbonate inan organic solvent at from about 0° to room temperature. Pyridine is aparticularly useful solvent as it also acts as a base, but methylenechloride is also useful. The amino-protecting group X, if present, isthen removed conventionally to produce compounds in which R is H: forexample a t-butoxycarbonyl protecting group is typically removed byreaction with trifluoroacetic acid at from about 0° C. to roomtemperature.

The compounds of the formula (I) in which R is other than H can also beprepared by the reaction of a compound of the formula (I) in which R isH (prepared as previously described) with a compound of the formula Q--Ror R--O--R where Q is a leaving group such as chloro and R is as definedfor formula (I) except for H. The reaction is again preferably carriedout in the presence of an organic or inorganic base and in a suitableorganic solvent, typically at from 0° C. to about room temperature.Pyridine is again the preferred solvent since it can also function as abase. However, methylene chloride is an alternative preferred solventand in this case triethylamine is the preferred base. The product (I)can then be isolated and purified conventionally.

Because in the benzimidazole end products (I) and starting materials(II) in which R is H, the position of the hydrogen atom at the nitrogenatom of the imidazole ring cannot be determined (tautomerism), it willbe appreciated that the compounds are correctly named as5(6)-substituted benzimidazoles.

Where the products (I) are prepared as mixtures of the 5- and 6- R¹-substituted compounds (e.g. as in Example 3), then the 5- and 6-compounds can be separated by conventional techniques such as byfractional recrystallisation and chromatography, particularlyreverse-phase hplc.

The starting materials (II) in which X is an amino-protecting group arepreparable by the N-protection of the corresponding benzimidazoleshaving a hydrogen atom at the 1-position with a suitable reagent, e.g.di-t-butyldicarbonate. These "unprotected" benzimidazoles, i.e. thecompounds (II) in which X is H, are known compounds and in many caseshave generic non-proprietory names, as follows: ##STR6##

For further details of these compounds please also see for example thefollowing references: S. Sharma et.al., Proc. Drug. Res., 1983, 27, 85;O. W. Ostmann et.al., Prog. Antimicrob. Anticancer Chemother, 1969, 1,159; A. H. M. Raeymaekers, Arzneim-Forsch/Drug. Res., 28(1), 586; E. A.Averkin et.al., J.Med. Chem, 1975, 18, 1164; S. Ram et.al., Org. Prep.Proced. Int, 1985, 17, 215; H. D. Brown et.al., JACS, 1961, 83, 1764; D.R. Hoff et.al., Experientia, 1970, 26, 550; U.S. Pat. No. 3,010,968, GB1123317; U.S. Pat. Nos. 3,915,986; 4,002,640; 4,435,418; 4,826,841;4,032,5361; 4,512,998; DE-A-3247615; EP-A-0387941; EP-A-0009174; andZA-7902975.

C₁ -C₆ Alkylthio groups represented by or present in R¹ can be oxidizedto C₁ -C₆ alkylsulfinyl or alkylsulfonyl groups by conventionaltechniques, e.g. by the use of 1 or more equivalents ofm-chloroperbenzoic acid, as appropriate, in a suitable solvent such asmethylene chloride.

The utility of the compounds as anthelmintics when given transdermallycan, for example, be assessed by the following technique:

Male Cobb-Wistar rats weighing 40-50 g (3-4 weeks old) are used. Theanimals are fed on normal cubed rodent diet containing 60 ppm of theimmunosuppressant hydrocortisone acetate. Immunosuppression commencesone week prior to infection and is maintained until necropsy. Both foodand water are given ad lib.

Each rat is given 1500 T. colubriformis infective larvae orally.Ovine-derived larvae are prepared from stock cultures immediately beforedosing and checked microscopically for viability. Only motile, viablelarvae are used. Parasites are administered in 0.25 ml of water.

One to three weeks post-infection animals are randomly assigned toeither treatment (generally 5 rats) or control (generally 10 rats)groups. Solutions of test compounds in appropriate vehicles (see below)are administered topically by pipette to a shaven area (approximately 1square inch) of the back close to the neck. Drug concentrations in thevehicle are adjusted such that each animal receives the desired dosagein <0.25 ml/100 g body weight. At the time of dosing the weight of theanimals ranges from 90 to 110 g. All animals are necropsied three dayspost-dosing.

At necropsy the small intestine of each animal is removed and placed ina plastic pot containing 20 ml of pepsin digest mixture, comprisingpepsin A powder 8 g, NaCl 8.5 g, plus 16 ml concentrated HCl in 1 L ofdistilled water. The digests are incubated at 37° C. for 4 hours priorto washing over a 75 um sieve with a high pressure water spray. Wormsretained on the sieve are collected by washing into fresh pots andstained using an iodine/potassium iodide solution comprising iodine 30g, potassium iodide 40 g, plus 30 ml methylated spirits in 70 mldistilled water. The contents of each pot is then diluted to a finalvolume of 500 ml with distilled water and a 50 ml aliquot taken for wormcounting. The efficacy of each drug treatment is determined as thepercent reduction from the average worm burden of untreated controls.

The following Examples illustrate the preparation of the compounds ofthe formula (I). The Preparation illustrates the preparation of astarting material.

Preparation 1 Preparation of2-(methoxycarbonylamino)-1-(t-butoxycarbonyl)-(5- and6-n-propylthio)benzimidazole

To a stirred suspension of methyl5(6)-n-propylthiobenzimidazole-2-carbamate(albendazole) (150 g, 0.57M)in 2 L of tetrahydrofuran was added 123 g (0.57M) of di-t-butyldicarbonate. The mixture was stirred for 18 hours at room temperatureand then for 5.5 hours at 50° C. A further 62 g of di-t-butyldicarbonate in 150 ml of tetrahydrofuran was then added. The mixture wasstirred for 18 hours at room temperature then for a further 2 hours at50° C. After evaporation, the residue was slurried with diethyl ether (1L) and filtered. The filtrate was evaporated and crystallized fromn-hexane to yield 66 g of a mixture of the title compounds. The filtercake was slurried with methylene chloride, filtered and the filtrate wasevaporated. The residue was crystallized from n-hexane to yield afurther 61 g of the title compounds.

Analysis: Found: C,55.91%; H,6.41%; N,11.58%. C₁₇ H₂₃ N₃ O₄ S requires:C,55.87%; H,6.34%; N,11.50%. M.Pt. 85°-87° C.

EXAMPLE 1 Preparation of 2[(Bis-methoxycarbonyl)amino]-(5(6)-n-propylthio)benzimidazole

To a stirred solution of2-(Methoxycarbonylamino)-1-(t-butoxycarbonyl)-(5- and6-n-propylthio)-benzimidazole (101.3 g, 0.28M, prepared as inPreparation 1) in 500 ml of pyridine at 0° C. was added 87 ml (1.12M) ofmethyl chloroformate over 30 minutes.

The mixture was allowed to warm to 20° C. and then stirred for 48 hours.A further 50 ml (0.64M) of methyl chloroformate was added over 30minutes with cooling. After stirring for 2 hours at 20° C. a further 57ml (0.73M) of methyl chloroformate was added and the reaction mixturestirred for 18 hours at 20° C. Then a further 50 ml (0.64M) of methylchloroformate was added along with 50 ml, of pyridine. After stirringfor 3 hours at 20° C, the reaction mixture was partitioned between ethylacetate (500 ml) and water (500 ml). The ethyl acetate layer was driedover sodium sulphate and filtered, then evaporated in vacuo. The residuewas treated with trifluoroacetic acid (400 ml) at -10° C., then allowedto warm to 20° C. and stirred for 1 hour. The reaction mixture wasevaporated in vacuo and the residue partitioned between ethyl acetate(400 ml) and saturated aqueous sodium bicarbonate solution (400 ml). Theethyl acetate layer was separated and washed with water (400 ml). Theaqueous layer was back-extracted with more ethyl acetate (200 ml) andthe combined organic layers were dried over sodium sulphate, filteredand evaporated to dryness. The residue was suspended in methylenechloride (200 ml) and filtered. The filtrate was evaporated to dryness.The residue was crystallized from diethyl ether and hexane to yield 60 gof the title compound.

Analysis %: Found: C, 51.65; H, 5.14; N, 12.92; C₁₄ H₁₇ N₃ O₄ Srequires: C, 52.00; H, 5.30; N, 12.99. M.Pt. 114.5°-117.7°.

EXAMPLE 2 Preparation of2-[(Bis-methoxycarbonyl)amino]-1-(n-butyloxycarbonl)-(5- and6-n-propylthio)-benzimidazole

To a stirred solution of2-[(bis-methoxycarbonyl)amino]-5(6)-n-propylthio)benzimidazole (1.0 g,3.1 mmol, see Example 1) in 5 ml of pyridine at 0° C. was added 0.8 ml(6.2 mmol) of n-butyl chloroformate. The mixture was then allowed towarm to 20° C. and stirred for 4 hours. The mixture was then partitionedbetween 1N hydrochloric acid (50 ml) and ethyl acetate (50 ml). Theethyl acetate layer was then washed with water and dried over magnesiumsulphate. Then the solution was filtered and evaporated to dryness invacuo. The residue was extracted with hot hexane and the extractcrystallized to yield 0.7 g of a mixture of the title compounds.

Analysis %: Found: C, 54.22; H, 6.33; N, 9.75; C₁₉ H₂₅ N₃ O₆ S requires:C, 53.90; H, 5.95; N, 9.92. M. Pt. 87.6°-90.5° C.

EXAMPLE 3 Preparation of2-[(Bis-methoxycarbonyl)amino]-1-(n-octyloxycarbonyl)-(5- and6-n-propylthio)benzimidazole

The procedure of Example 2 was followed but using n-octyl chloroformate(6.6 g, 34 mmol) instead of n-butyl chloroformate and the other reagentspro rata to yield 7 g of a mixture of the title compounds as an oil.

Analysis %: Found: C, 57.71; H, 6.48; N, 8.39; C₂₃ H₃₃ N₃ O₆ S requires:C, 57.60; H, 6.94; N, 8.76. M. Pt. 65°-67° C.

EXAMPLE 4 Preparation of2[(Bis-methoxycarbonyl)amino]-1-(cholester-3-yloxycarbonyl)-(5- and6-n-propylthio) benzimidazole

To a solution of2-[(bis-methoxycarbonyl)amino]-(5(6)-n-propylthio)benzimidazole (5 g,15.5 mmol) in 100 ml of methylene chloride was added 7.6 g (17 mmol) ofcholester-3-yl chloroformate and 2.4 ml (17 mmol) of triethylamine. Themixture was then stirred at 20° C. for 2 hours, evaporated in vacuo, andthe residue was suspended in diethyl ether and filtered. The filtratewas then passed through a plug of silica (Merck, "silica gel 60", [TradeMark] 25 g) and washed off with more ether. The filtrate was evaporatedin vacuo to yield a mixture of the title compounds, 11 g.

Analysis %: Found: C, 68.99; H, 8.68; N, 5.31; C₄₂ H₆₁ N₃ O₆ S requires:C, 68.54; H, 8.35; N, 5.71. M. Pt. 65°-67° C.

EXAMPLE 5

Preparation of2-[(Bis-methoxycarbonl)amino]-1-(5-[t-butyloxycarbonl]pentyloxycarbonyl)(5-and 6-n-propylthio)benzimidazole and the corresponding1-(5-carboxypentyloxycarbonyl) compounds

To a stirred suspension of t-butyl 6-hydroxyhexanoate (J. Org. Chem.,1980, 45, 3081-3084) (1.0 g, 2.4 mmol), potassium carbonate (0.4 g, 7.8mmol) in toluene (10 ml) at 0° C. was added, dropwise over 10 minutes,2.7 ml (3.12 mmol) of a 12.5% solution of phosgene in toluene. Themixture was stirred at 0° C. for 30 minutes then allowed to warm to 20°C. and stirred for 1 hour. The mixture was then purged with nitrogen for1 hour and evaporated in vacuo. The product was filtered throughmagnesium sulphate, washed with dry ether and evaporated in vacuo. Theresidue was added to a solution of2-[(bis-methoxycarbonyl)amino]-5(6)-n-propylthio)benzimidazole (0.38 g,1.2 mmol) in pyridine (5 ml) at 0° C. with stirring. The mixture wasthen allowed to warm to 20° C. and stirred for 18 hours. The mixture wasthen partitioned between diethyl ether (50 ml) and 1N hydrochloric acid(50 ml). The ether layer was dried over sodium sulphate, filtered andevaporated in vacuo. The product was purified by chromatography onsilica (Merck, "silica gel 60" Trade Mark, 25 g,) , eluting with diethylether/hexane (80/20) to yield 0.26 g of a mixture of the title compoundsas the t-butyl esters.

The free acids were obtained by treatment of the mixture of the esterswith trifluoroacetic acid (10 ml) followed by evaporation in vacuo toyield 0.1 g of a mixture of the title acids.

EXAMPLE 6 Preparation of2-[(Bis-methoxycarbonyl)amino]-1-(methoxycarbonyl)-(5- and6-n-propylthio)benzimidazole

To a slurry of albendazole (25 g, 0.19M) in 200 ml of pyridine was added50 ml (0.65M) of methyl chloroformate, dropwise, at 0° C. The mixturewas allowed to warm to 20° C. and stirred at this temperature for 1hour, then partitioned between ethyl acetate (200 ml) and 1Nhydrochloric acid (200 ml). The ethyl acetate layer was dried overmagnesium sulphate, filtered and evaporated. The residue was extractedwith hot hexane and the extract crystallized to yield. 11.4 g of amixture of the title compounds.

Analysis %: Found: C, 50.51; H, 4.51; N, 10.96; C₁₆ H₁₉ N₃ O₆ Srequires: C, 50.39; H, 4.99; N, 11.02. M. Pt. 83.2°-85.8° C.

EXAMPLE 7

Preparation of 2-[(Bis-methoxycarbonyl)amino]-1-(methoxycarbonyl)-(5-and 6-phenylthio)benzimidazole

The procedure of Example 6 was followed but using fenbendazole (5.0 g,17 mmol) instead of albendazole, and the other reagents pro rata, toyield 4.2 g of a mixture of the title compounds.

Analysis %: Found: C, 54.80; H, 4.10; N, 10.27; C₁₉ H₁₇ N₃ O₆ Srequires: C 54.93; H, 4.12; N, 10.17. M. Pt. 140.5°-147.2° C.

We claim:
 1. A compound of formula (I) ##STR7## or their non-toxic salt,in which R is H, --CO₂ (C₁ -C₁₀ alkyl), --CO₂ (cholester-3-yl) or agroup of the formula --CO₂ (CH₂)_(n) COOH or --CO₂ (CH₂)_(n) CO₂ (C₁ -C₆alkyl) in which n is an integer of from 1 to 10;R¹ is either (i)benzoyl, phenyloxy, phenylthio, phenylsulfinyl, phenylsulfonyl,phenylsulfonyloxy, C₁ -C₆ alkylthio, C₁ -C₆ alkylsulfinyl, C₁ -C₆alkylsulfonyl or (C₃ -C₇ cycloalkyl)carbonyl, said phenyl groups, andthe phenyl portion of said benzoyl group, optionally having 1 to 3substituents each independently selected from halo, C₁ -C₄ alkyl,halo(C₁ -C₄ alkyl), C₁ -C₄ alkoxy, C₁ -C₄ alkylthio, C₁ -C₄alkylsulfinyl, C₁ -C₄ alkylsulfonyl, C₂ -C₄ alkanoyl, nitro,isothiocyanato, and cyano; or (ii) a group of the formula: ##STR8##where X is O,S,SO,SO₂ or NR⁴ in which R⁴ is hydrogen, C₁ -C₄ alkyl,phenyl or phenyl(C₁ -C₄ alkyl), said phenyl groups being optionallysubstituted by 1 or 2 substituents each independently selected from C₁-C₄ alkyl, halo, hydroxy and C₁ -C₄ alkoxy; and R₅ is H, C₁ -C₄ alkyl,halo, hydroxy or C₁ -C₄ alkoxy; ##STR9## R¹ being in the 5(6)-positionwhen R is H, and in the 5- or 6-position when R is other than H; and R²and R³ are each independently --CO₂ (C₁ -C₄ alkyl).
 2. A compoundaccording to claim 1, in which n is from 1 to
 3. 3. A compound accordingto claim 1, in which R is H, --CO₂ (C₁ -C₈ alkyl), --CO₂(cholester-3-yl), --CO₂ (CH₂)_(n) COOH or --CO₂ (CH₂)_(n) --CO₂ --(C₁-C₄ alkyl).
 4. A compound according to claim 3, in which R is H or --CO₂(C₁ -C₄ alkyl).
 5. A compound according to claim 1, in which said alkylgroups in R have from 1 to 4 carbon atoms.
 6. A compound according toclaim 1, in which R¹ is C₁ -C₄ alkylthio, C₁ -C₄ alkylsulfinyl,phenylthio, phenylsulfinyl, benzoyl optionally substituted by halo,phenylsulfonyloxy optionally substituted by halo, or1,2-benzisoxazol-3-yl.
 7. A compound according to claim 6, in which R¹is benzoyl, 4-fluorobenzoyl, 4-fluorophenylsulfonyloxy, n-propylthio,n-propylsulfinyl, phenylthio, phenylsulfinyl or 1,2-benzisoxazol-3-yl.8. A compound according to claim 7, in which R¹ is n-propylthio.
 9. Acompound according to claim 1, in which R² and R³ are both --CO₂ CH₃.10. An anthelmintic composition comprising a compound as claimed inclaim 1 and a pharmaceutically or veterinally-acceptable carrier.
 11. Ananthelmintic pour-on or spot-on composition for application to the skinof an animal, which comprises a compound according to claim 1 and aveterinally-acceptable carrier effective for passing the compoundthrough the skin of the animal.
 12. A method of combating helminths inan animal, which comprises applying to the skin of said animal an amountsufficient to exert an anthelmintic effect of a compound according toclaim 1 whereby said compound is absorbed through the skin.
 13. A methodof combating helminths in an animal, which comprises administeringorally or parenterally to said animal an anthelmintically effectiveamount of a compound according to claim 1.